Capillary refrigerating systems



M. c. STEVENS 2,956,421

CAPILLARY REFRIGERATING SYSTEMS Filed April 4. 1957 Oct. 18, 1960 & x

INVENTOR. Mme/v C. STEVE/V5 BY g w ATTOR United States Patent "ice CAPILLARY REFRIGERATING SYSTEMS Myron C. Stevens, Mount Wolf, Pa., asignor to Borg- Warner Corporation, Chicago, 111., a corporation of Illinois Filed Apr. 4, 1957, Ser. No. 650,757 Z'Claims. (Cl. 62-511) This invention relates to refrigerating systems and more particularly to such systems having a capillary fed evaporator.

In a refrigerating system some means must be provided for maintaining the differential in pressure between the evaporator and the condenser of the system, and also for metering the flow of refrigerant from the condenser to the evaporator. This can conveniently take the form of a capillary or restrictor tube. Such a capillary tube has the advantages of low cost and trouble-free operation.

However, in such a capillary, the refrigerant leaving the capillary and discharging into the evaporator comprises a mixture of liquid and gas. This has the eflect of producing undesirable noises both due to the higher velocity of the mixture flow through the capillary due to the gas therein and the fact that gaseous globules or pockets of refrigerant form within the evaporator and then collapse.

It is an object of the invention, therefore, to provide a refrigerating system including a capillary fed evaporator wherein refrigerant noises are considerably reduced.

It is a further object to provide a refrigerating system including a capillary fed evaporator wherein refrigerant is discharged into the evaporator in such a manner as to create a turbulent eflect thereon.

It is yet another object to provide a refrigerating system including a capillary fed evaporator wherein the refrigerant discharging from the capillary into the evaporator is subcooled prior to such discharge recondensing gaseous refrigerant therein, the capillary being so arranged that an area of turbulence is created within the evaporator into which area the discharging refrigerant is directed.

Yet another object of the invention is to provide a refrigerating system including a capillary fed evaporator, the evaporator including a closed end, and means for discharging refrigerant from the capillary against said closed end.

In carrying out the invention, the capillary is inserted into the evaporator for some portion of its length. The refrigerant mixture flowing through this portion of the capillary is then sub-cooled prior to its discharge to recondense a portion of the gaseous refrigerant. In addition, the capillary is so arranged that it discharges against an end wall of the evaporator. This effects a further noise reduction due to the creation of a turbulent effect on the discharging refrigerant.

The invention consists of the novel constructions, arrangements, devices and methods to be hereinafter described and claimed for carrying out the above-stated objects and such other objects as will appear from the following description of preferred embodiments of the invention illustrated with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a refrigerating system embodying the invention;

Fig. 2 is a sectional view on an enlarged scale taken 2,956,421 Patented Oct. 18, 1960 on line 2-2 of Fig. 1, showing a preferred form of a capillary discharging into an evaporator, according to the invention;

Fig. 3 is a side view of the capillary prior to its insertion in the evaporator; and

Fig. 4 is a diagrammatic view of a refrigerating system embodying an alternate embodiment of the invention.

Referring now to Fig. 1, a refrigerating system embodying the invention comprises a compressor 10 driven by a motor 11. A condenser 12 and an evaporator 13 are provided to complete the basic components of the refrigerating system. The discharge of the compressor 10 is connected .to the condenser 12 by way of a hot gas -line 14. The evaporator 13 is connected to the inlet of compressor 10 by way of a cold gas line 15. Condenser 12 and evaporator 13 are connected together by means of a restrictor or capillary tube 16.

The end of evaporator 13 connected to the capillary 16 is closed by a connector 17 brazed thereto, as indicated at 18. A passageway 19 is provided in connector 17 for receiving the capillary tube 16. The capillary tube 16 extends through the passageway 19, as can be clearly seen in Fig. 2, and is brazed to the connector 17 at 20.

Immediately adjacent the connector 17, the end of the capillary tube is bent, as shown at 21. A second reversed bend 22 is provided so that the capillary lies adjacent the inner Wall of the evaporator 13. The end of the capillary is turned on itself, as at 23, and terminates in a free :end portion 24, so that refrigerant leaving the end .portion 24 of the capillary discharges against connector 17.

The capillary, prior to its insertion within the evaporator 13, takes the form shown in Fig. 3. The distance h is greater than the inside diameter of the evaporator -13 so that when the capillary is pressed into its position in the evaporator the free end portion 24 is placed under a compressive force so that the capillary fits snugly within the evaporator adjacent the walls thereof and does not vibrate therein. This has the further effect of consistently locating the free end of the capillary.

In operation, liquid refrigerant evaporated Within evap orator 13 flows through cold gas line 15 to the inlet of compressor 10. After being compressed within the compressor, the now high pressure gas flows through hot gas line 14 and into condenser 12 where it is condensed to a liquid. The liquid then flows through capillary 16 and into evaporator 13 to complete the cycle.

Capillary 16 serves two primary functions: (1) it serves to maintain the differential in pressure between the condenser and evaporator of the refrigerating system and (2) it serves as a metering device to meter the refrigerant from the condenser to the evaporator. It is apparent that the flow rate through the capillary may be varied by varying the length thereof and also the inside diameter. However, once this flow rate has been established for .a particular system by fixing the inside diameter and length of the tube, it obviously remains a constant for a given set of ambient conditions. In designing the capillary, a condenser and evaporator temperature are selected as being representative of the average conditions under which the equipment must operate.

In a refrigerating system as set out above, properly charged with a suflicient amount of refrigerant, and operating at the 'average conditions for which the capillary was designed, liquid refrigerant free of gas enters the capillary from the condenser. In its passage through the capillary from condenser pressure to evaporator pressure, however, a certain portion of the refrigerant flashes into gas, so that a mixture of gaseous and liquid refrigerant is usually emitted from the discharge end of the capillary. The velocity of [the refrigerant mixture leaving the capillary varies as the proportion of gas therein varies; the greater the amount of gas therein, the greater the velocity. A hissing noise is generally produced by the rnixture discharging from the capillary. The intensity of the noise varies as the discharging velocity of the mixture varies; the greater the. discharging: velocity, the greater the noise intensity. It will be apparent, therefore,

, that the hissing noise produced by the discharging refrigerant will increase as the discharge velocity of the refrigerant increases.

a The system will operate with fairly good efficiency over a range of conditions both more and less severe than the design conditions. Quite often, however, the condensing ambient temperature is such that a mixture of gas and liquid refrigerant enters the capillary from the condenser. I This will greatly increase the proportion of gas-to-liquid of. the refrigerant as it issues from the discharge end of the capillary. As pointed. out above, this has the effect of intermittently increasing the velocity of flow through the capillary, increasing the intensity of the hissing noise produced by the higher velocity mixture discharging from the capillary 16 into the evaporator;

In addition to the above hissing noise, there is a further noise efie'ct dueparticularly, I believe, to globules of gas forming withinthe evaporator, when the refrig erant mixture discharges from the capillary into the con sid'erably larger evaporator passage, and then collapsing with the" attendant noises. This noise is quite apart from the hissing noise produced by the high velocity mixture discharging from the capillary and is quite independent of velocity.

1 It is wellknown, of course, that considerable noise can be eliminated by sub-cooling the refrigerant within the capillary before it emerges into the evaporator 13. Thissub-cooling hasthe effect of recondensing the gas mixedin with the liquid refrigerant. I have provided for thissub-cooling of [the refrigerant by' inserting a relatively large portion of the capillary into the evaporator so that refrigerant passing there through is subjected to a refrigerating eliect once it passes bend 21- and until the time it discharges from the end of the capillary, 'all as is well known in the art. It will be appreciated that the amount of sub-cooling varies with the amount of capillary lying within the evaporator. An optimum length can be determined empirically beyond which length no appreciable improvement in the noise level will be observed;

In addition to the above, I have discovered that the general noise level can be considerably reduced by discharging the refrigerant into the pocket formed between the evaporator Walls and connector 17 and against connector 17. I believe that the reason this reduces the noise level is that it sets up a turbulent-region slowing the velocity. of discharge of the mixture of liquid and gas and also either preventing the formation of globules of gas within the evaporator or else collapsing such globules before they have a chance to enlarge to a size sufiicient to create an appreciable noise.

In any event, I have discovered that the closer" the end of the capillary is to the connector 17-, the greater is the reduction in the noise level. The only limiting factor is, of course, that the end of the capillary must not be so close to the connector 17' as. to restrict the flow through the evaporator.

In. addition, I believe that the creation. of turbulence is aided by the fact that the refrigerant flow must be reversed before it can flow"'through the evaporator.

In Fig. 4 I show an alternative embodiment in which the same results of sub-cooling the refrigerant and creating a turbulent area within the evaporator are achieved. This is done, however, without the necessity of reversing the capillary onf itself; In einbodinient,--the end of the evaporator 13 is closed by aplugZS. The evaporator is, in effect, reversed with respect to the capillary 16. The capillary 16 then'passes through an aperture 26 provided in the wall of the evaporator 13 and terminates at the desired distance from cnd plug 25. Aperture 26 is thenclosed around. the capillary by some method, such as brazing, soldering, etc."

It will be appreciated that the refrigerant flowing within the capillary is sub-cooled in its passage through the capillary once 'it'haspassed: the: aperture 26; The mixture leaving. the capillary discharges against end plug 25 producing a turbulent area with the desired; effect of slowing the velocity of the mixture and collapsing gaseous globules formed within: the evaporator.

It will apparent that L have provided, in a simple, expeditiousand. extremely low" cost: manner, a device which. functions efiiciently and reliably to reduce thenoise level i'rra refrigerating system-. This. problem of noise reduction in' refrigerating systems, particularly in: their use; within the'home, is one that has always plagued industry; Yet,v for but a: minuteincrease incest, I have devised a method for substantially reducing refrigerant noises within an evaporator contributing: greatly to an overall noise" reduction in the operation of such a system.

L wish it to beunderstood that myiinventiorr is not: to be limited to. the specific constructions andarrangements shown and described, except only insofar as the claims may be so limited,.as itwill be apparentto those skilled in the art that changes may bemade without departing from: the principles of the invention.

What is claimed is:

l. I-ni a. refrigerating system, an evaporator having a eloserlcend; a restrictor tuhe extending'through saidclosed end. into said evaporator: and connected thereto, said restrictor-tube being. turned back: on itself to form a U-shaped pcnrtiorr. discharging. refrigerant. against. said closed. end;

2; In a refrigerating system, an. evaporator having a closed;crrd,-a restrictor tube extending through said closed end :into 'saaidt evaporator and connected. thereto, said restrictor'tube. being Ltnrned' back on itself to form a l- J-shapedi' portion discharging refi-i'gerant against said closed end, the width of said U-shaped portionin an unstressed condition being greatertthan the inside diameter of's-ai'dievaporatorz' J I I References Cited in the file of this patent UNITED STATES PATENTS 2,785,542 Thomas" Mar; 19,1957 

